Type: Trees & Vines
Difficulty: Hard
Season: Fall
Sowing: Plant a sapling

Trees & Vines

Ginkgo Nut

Ginkgo biloba

Ginkgotoxin, starch · a seed eaten cooked, and only a few at a time

The ginkgo nut is the seed of the ginkgo tree. The yellow flesh around it is not fruit pulp but an outer seed coat, notorious for its smell and capable of reddening bare skin. Crack the hard white shell inside and you find the pale green kernel, which is the part people eat. Ginkgo makes up a large share of Korea's street trees, so the seeds are everywhere in autumn, but roadside fruit sits in exhaust and heavy metals and is better left alone. The Donguibogam recorded ginkgo as toxic, said raw nuts stabbed at the throat, and warned that children who ate them were seized with fright.

Year-Round Calendar

Sowing

Harvest

Where It Grows

Origin Major producer Latitudes at 15–25℃ Zoom and pan to explore · temperatures are rough zonal averages

Origin A near-wild population survives on Mount Tianmu in Zhejiang, while Taixing in Jiangsu and Tancheng in Shandong are the nut-producing districts. They account for most of the world's supply.
Major producer The tree is widely planted along streets and as a village shade tree, so more of the crop is gathered from what falls in autumn than harvested from orchards. Harvest October, November
10. 10
11. 11
Major producer In Aichi, Fukuoka and elsewhere, trees are planted and raised specifically to harvest the nuts.

A tree that once survived only in the mountains of southern China was carried by human hands to Korea and Japan, and from there to cities around the world. It is the sole surviving species in the order Ginkgoales, which is why it is called a living fossil. For extracting compounds from the leaves, southwestern France and the southeastern United States have their own large plantations grown for leaves alone, so the regions that produce the nuts and the regions that produce the leaves are not the same.

Optimum: 15~25℃
Range: 5~30℃
Hardiness: Hardy

A temperate deciduous tree of large stature, it endures cold approaching -30℃ as well as the exhaust fumes and wind of the city. It is not fussy about soil, but its roots run deep and spread wide, so it will not last more than a few years in a pot. Seeds form only on female trees, and a male tree must stand nearby for them to ripen.

Harvested 5–25 years after planting. Grown from seed, a tree takes more than twenty years to bear fruit; a grafted tree bears in five or six. The year of planting and the year of harvest lie far apart.

In Korea Nationwide

Across the country it is planted as a street tree and a village shade tree, and few places plant it in orchards to harvest the nuts. Seeds form only on female trees.

How to grow

Light: For open ground only; it is not a pot plant. It needs an open site in sun all day.
Soil and depth: For open ground only. It is not fussy about soil, but the roots run deep and wide and a pot will not hold it for more than a few years.
Spacing: Eight to ten metres in the ground. Pot culture is effectively impossible, and even as bonsai it will not fruit.
Watering: Water for the first two or three years after planting; after that rainfall is enough. Long droughts scorch the leaf tips.
Feeding: A ring of compost around the trunk in early spring is all it needs. Heavy feeding is unnecessary.
Harvest: October into November. Collect them once the outer coat has yellowed, softened, and dropped. Soak three days to rot the coat off, rub it away, then wash and dry the shells. Wear rubber gloves for this: the ginkgolic acid in the yellow coat causes contact dermatitis on bare skin.

What makes the difference. This will not work in a pot; buying is the realistic route. Choose shells that are a pale cream rather than bleached white, and that make no rattle when you shake them. A rattle means the kernel has dried and shrunk. To open them, roll them in a dry pan with a pinch of salt over medium heat for five minutes, or microwave them in a paper bag for a minute, scoring each shell first so they do not burst. The thin inner skin rubs off with a damp paper towel.

Why this one is harder. A mature tree passes twenty metres with deep roots. Only female trees bear seed, and sex is not reliably known until it fruits.

Common problems

Ginkgo scale insect You will see Grey shell-like growths along the branches and early leaf drop. What to do Apply horticultural oil in winter and cut out badly infested branches.
Powdery mildew You will see A white dust settling on the leaves of young trees. What to do It mostly hits crowded nursery stock. Widen the spacing and clear the lower leaves.
Root rot You will see Leaves yellowing for no obvious reason and growth stalling. What to do It comes from standing water. Build a drainage layer at planting and do not bury the trunk deep.

This page describes how a crop is grown and used. It does not claim health effects for any food, nor is it intended to prevent or treat disease. Component and study notes are references only and do not mean the same result occurs in people. Consult a medical professional about health concerns.

Health Benefits

What the old record says. Ginkgo appears in the Donguibogam's fruit section as eunhaeng. The entry attaches the caveat that it is cold in nature and toxic, and warns in the same passage against eating the nuts raw. This is a record from a seventeenth-century medical text, not a modern medical judgement.

What is known today - leaf extract research is a separate matter. A number of studies have been reported on extracts made from ginkgo leaves, but that research was conducted on an extract, and both the material and the conditions differ from eating the kernel. Leaf extract is regulated separately as a medicine or a functional food, and brewing ginkgo leaves at home is not advised. For the kernel eaten as food, what has been established amounts to its composition and the limits on how much is eaten at one time.

Nutrition

Ginkgotoxin (4'-O-methylpyridoxine, higher in uncooked kernels) — Poisoning cases have been reported after eating large amounts
Starch (The main component of the roasted kernel) — Gives a texture close to chestnut
Ginkgolic acid (The irritant in the yellow outer flesh) — Can cause contact dermatitis if handled bare-handed
Protein (About 4 g per 100 g of raw kernel) — Closer to grain than to nuts in composition

Ginkgotoxin and how many you eat Ginkgo kernels contain ginkgotoxin, or 4'-O-methylpyridoxine. It interferes with the action of vitamin B6, and cases of poisoning with vomiting and convulsions after eating large amounts have been reported for a long time. Ginkgotoxin stands up well to heat and survives roasting and boiling. Reported cases cluster in young children, so do not give ginkgo nuts to a child under five. Older children should stay within one or two cooked nuts, and adults should not go past ten in a day. Nobody eats them raw. The Donguibogam likewise called ginkgo toxic and warned about children.

Starch and calories Roasted ginkgo is mostly starch, closer to a chestnut than a nut. Raw kernels run about 180 kcal per 100 g, far lighter than tree nuts. Low calories are not a licence to eat more of it, though. The limit here is set by the count, not the calories.

Ginkgolic acid in the outer coat The ginkgolic acid in the yellow outer coat belongs to the same family of irritants as poison ivy and lacquer tree sap. Handling it bare-handed can produce a red, itchy contact dermatitis. Sensitivity varies widely, and people who react once often react more strongly the next time. Put rubber gloves on before you start collecting.

Pairings

○ Rice and porridge — A few roasted kernels stirred into rice add colour and a bit of bite. The small quantity also keeps you from overdoing it. Shelled ginkgo yellows fast, so peel it just before use.

○ Grilled skewers — Threaded onto a soy-glazed skewer, ginkgo gives a plain counterpoint to the rich meat. Two or three per skewer is enough. Grilled too long, the centres dry out.

○ Steamed egg — Halved kernels give something to bite in an otherwise soft dish. Cook them first so the colour stays clear.

△ Cooking does not remove it — none under five, ten a day at most for adults — The ginkgotoxin (4'-O-methylpyridoxine) in the kernel stands up well to heat and survives roasting and boiling. Cooking is not a licence to eat freely; even cooked nuts are counted out. Reported poisonings cluster in young children, so do not give them to anyone under five. Older children should stay within one or two cooked nuts, and adults should not go past ten in a day. Nobody eats them raw. The riskiest setting is a bowl of roasted nuts picked at through a long evening, because nobody is counting. If vomiting or convulsions follow a large serving, seek medical care at once.

Varieties

Female tree (a sex, not a cultivar) (Sapling) — The one that bears fruit. Planted less often as a street tree because of the smell.
Male tree (a sex, not a cultivar) (Sapling) — Bears no fruit. Recent street plantings are mostly replaced with males.
Grafted ginkgo (Sapling) — An edible line with large kernels. Being grafted, it fruits sooner.

Source: Donguibogam, Fruit Section (銀杏) · Rural Development Administration (nongsaro.go.kr)